With the rapid increase of areal density and data rate for magnetic recording systems, the examination of high frequency switching dynamics of the recording medium becomes even more important. However, one of the biggest challenges is the lack of an ultrafast magnetic field pulse source with a large amplitude (>1 Tesla) and short rise-time (<100 ps). Conventional recording heads capable of generating large fields are typically limited by the precession frequency of the magnetization direction in the write pole, even when driven by a waveguide. Other options like high bandwidth co-planar waveguides have difficulty generating a large amplitude pulse field. Optical pulse excitation of a Schottky barrier can deliver an ultrafast pulse, but the amplitude is well below 1 kOe. The Stanford Linear Accelerator can also deliver such short pulse fields with large amplitudes, but it cost millions of dollars.
It has been shown that the magnetization of ferromagnetic (FM) thin films can be modulated on a sub-picosecond timescale by photoexciting the electron spins away from their equilibrium position with the lattice, thereby creating an non-equilibrium condition such that Te>>T1 and Ts>>T1, where Te, Ts and T1 are temperatures defined in terms of a three-temperature model, specifically designated for the sub-system of electron, spin and lattice degrees of freedom of the spin-polarized magnetic systems. However the application of fast heat pulses on such ordinary ferromagnetic material can only result in a demagnetizing field, where the photoexcitation terminates the fringing field for a short period.
There is a need for a transducer that can provide fast magnetic field pulses at a magnetic field strength that would be useful in practical devices.